Integrated circuit that controls a search space setting process

ABSTRACT

An integrated circuit, for example, included in a wireless communication base station, controls a process that includes mapping a first downlink control channel to control channel element(s) (CCE(s)) in a first search space comprised of a first plurality of CCEs, the first downlink control channel including resource assignment information, which indicates a resource allocated to a terminal in a component carrier n (CC n ) out of one or more component carrier(s) (CC(s)), and mapping a second downlink control channel to CCE(s) in a second search space comprised of a second plurality of CCE(s), the second downlink control channel including resource assignment information, which indicates a resource allocated to the terminal in a component carrier n+1 (CC n+1 ) out of the CC(s), the first plurality of CCEs and the second plurality of CCEs are consecutive. The process also includes transmitting the first and the second downlink control channels to the terminal.

BACKGROUND Technical Field

The present invention relates to a radio communication base stationapparatus, a radio communication terminal apparatus and a search spacesetting method.

Description of the Related Art

3GPP-LTE (3rd Generation Partnership Project Radio Access Network LongTerm Evolution, hereinafter referred to as “LTE”) adopts OFDMA(Orthogonal Frequency Division Multiple Access) as a downlinkcommunication scheme and adopts SC-FDMA (Single Carrier FrequencyDivision Multiple Access) as an uplink communication scheme (e.g., seenon-patent literatures 1, 2 and 3).

According to LTE, a radio communication base station apparatus(hereinafter abbreviated as “base station”) performs communication byallocating resource blocks (RBs) in a system band to a radiocommunication terminal apparatus (hereinafter abbreviated as “terminal”)per time unit called “subframe.” Furthermore, the base station transmitscontrol information for notifying results of resource allocation ofdownlink data and uplink data to the terminal. This control informationis transmitted to the terminal using a downlink control channel such asPDCCH (Physical Downlink Control Channel). Here, each PDCCH occupies aresource made up of one or a plurality of continuous CCEs (ControlChannel Elements). LTE supports a frequency band having a width ofmaximum 20 MHz as a system bandwidth.

Furthermore, the base station simultaneously transmits a plurality ofPDCCHs to allocate a plurality of terminals to one subframe. In thiscase, the base station includes CRC bits masked (or scrambled) withdestination terminal IDs to identify the respective PDCCH destinationterminals in the PDCCHs and transmits the PDCCHs. The terminal demasks(or descrambles) the CRC bits in a plurality of PDCCHs which may bedirected to the terminal with the terminal ID of the terminal andthereby blind-decodes the PDCCHs and detects a PDCCH directed to theterminal.

Furthermore, studies are being carried out on a method of limiting CCEsto be subjected to blind decoding for each terminal for the purpose ofreducing the number of times blind decoding is performed at theterminal. This method limits a CCE area to be subjected to blinddecoding (hereinafter referred to as “search space”) for each terminal.Thus, each terminal needs to perform blind decoding only on CCEs in asearch space allocated to the terminal, and can thereby reduce thenumber of times blind decoding is performed. Here, the search space ofeach terminal is set using the terminal ID of each terminal and a hashfunction which is a function for performing randomization.

Furthermore, as for downlink data from the base station to the terminal,the terminal feeds back an ACK/NACK signal indicating an error detectionresult of the downlink data to the base station. The ACK/NACK signal istransmitted to the base station using an uplink control channel such asPUCCH (Physical Uplink Control Channel). Here, studies are being carriedout on associating CCEs with a PUCCH to eliminate the necessity ofsignaling for notifying the PUCCH used to transmit an ACK/NACK signalfrom the base station to each terminal and thereby efficiently usedownlink communication resources. Each terminal can decide a PUCCH usedto transmit an ACK/NACK signal from the terminal from the CCE to whichcontrol information directed to the terminal is mapped. The ACK/NACKsignal is a 1-bit signal indicating ACK (no error) or NACK (errorpresent), and is BPSK-modulated and transmitted.

Furthermore, standardization of 3GPP LTE-Advanced (hereinafter referredto as “LTE-A”) has been started which realizes further speed enhancementof communication compared to LTE. LTE-A is expected to introduce a basestation and a terminal (hereinafter referred to as “LTE+terminal”)communicable at a wideband frequency of 40 MHz or above to realize adownlink transmission rate of maximum 1 Gbps or above and an uplinktransmission rate of maximum 500 Mbps or above. Furthermore, the LTE-Asystem is required to accommodate not only an LTE+terminal but alsoterminals compatible with the LTE system.

LTE-A proposes a band aggregation scheme whereby communication isperformed by aggregating a plurality of frequency bands to realizecommunication in a wideband of 40 MHz or above (e.g., see non-patentliterature 1). For example, a frequency band having a bandwidth of 20MHz is assumed to be a basic unit (hereinafter referred to as “componentband.” Therefore, LTE-A realizes a system bandwidth of 40 MHz byaggregating two component bands.

Furthermore, according to LTE-A, the base station may notify resourceallocation information of each component band to the terminal using adownlink component band of each component band (e.g., non-patentliterature 4). For example, a terminal carrying out widebandtransmission of 40 MHz (terminal using two component bands) obtainsresource allocation information of two component bands by receiving aPDCCH arranged in the downlink component band of each component band.

Furthermore, according to LTE-A, the amounts of data transmission on anuplink and downlink are assumed to be independent of each other. Forexample, there may be a case where wideband transmission (communicationband of 40 MHz) is performed on a downlink and narrow band transmission(communication band of 20 MHz) is performed on an uplink. In this case,the terminal uses two downlink component bands on the downlink and usesonly one uplink component band on the uplink. That is, asymmetriccomponent bands are used for the uplink and downlink (e.g., seenon-patent literature 5). In this case, both ACK/NACK signalscorresponding to downlink data transmitted with the two downlinkcomponent bands are transmitted to the base station using ACK/NACKresources arranged on a PUCCH of one uplink component band.

CITATION LIST Non-Patent Literature

-   NPL 1

3GPP TS 36.211 V8.3.0, “Physical Channels and Modulation (Release 8),”May 2008

-   NPL 2

3GPP TS 36.212 V8.3.0, “Multiplexing and channel coding (Release 8),”May 2008

-   NPL 3

3GPP TS 36.213 V8.3.0, “Physical layer procedures (Release 8),” May 2008

-   NPL 4

3GPP TSG RAN WG1 meeting, R1-082468, “Carrier aggregation LTE-Advanced,”July 2008

-   NPL 5

3GPP TSG RAN WG1 meeting, R1-083706, “DL/UL Asymmetric Carrieraggregation,” September 2008

BRIEF SUMMARY Technical Problem

When a plurality of downlink component bands and uplink component bandsfewer than the plurality of downlink component bands are used as in theabove described prior art (when asymmetric component bands are usedbetween the uplink and downlink), it is necessary to secure PUCCHs(ACK/NACK resources) to allocate ACK/NACK signals corresponding todownlink data for each of the plurality of downlink component bands forthe uplink component bands. When PUCCHs (ACK/NACK resources) associatedwith CCEs for each of all downlink component bands are secured, theamount of resources required for the PUCCHs becomes enormous in theuplink component bands. Therefore, the amount of resources secured foruplink resources (e.g., PUSCH (Physical Uplink Shared Channel)) to whichuplink data of the terminal is allocated decreases, and therefore datathroughput deteriorates.

Thus, a PUCCH (ACK/NACK resource) arranged in one uplink component bandmay be shared between a plurality of downlink component bands, that is,one PUCCH (ACK/NACK resource) may be secured for all component bands. Tobe more specific, PUCCHs corresponding in number to CCEs per downlinkcomponent band (or maximum number of CCEs between a plurality ofdownlink component bands) are secured for the uplink component bands.CCEs of the same CCE number of each downlink component band are thenassociated with the same PUCCH. Thus, the terminal transmits an ACK/NACKsignal corresponding to downlink data using a PUCCH (ACK/NACK resource)associated with a CCE regardless of the CCE of the downlink componentband with which the downlink data is allocated.

A case will be described as an example where the terminal uses twocomponent bands (component band 1 and component band 2). When performingwideband transmission (e.g., communication band of 40 MHz) only on adownlink, the terminal uses, for example, downlink component bands ofboth component band 1 and component band 2 on the downlink, while on anuplink, the terminal uses only an uplink component band of componentband 1 without using an uplink component band of component band 2.Furthermore, here, CCEs assigned the same CCE number (e.g., CCE #1, #2,. . . ) are arranged in the two downlink component bands so as to beable to accommodate LTE terminals. Furthermore, in the uplink componentband, for example, PUCCH #1 associated with CCE #1 and PUCCH #2associated with CCE #2 are arranged. Thus, CCEs #1 of the same CCEnumber arranged in the downlink component band of component band 1 andthe downlink component band of component band 2 respectively arecommonly associated with PUCCH #1. Likewise, CCEs #2 of the same CCEnumber arranged in the downlink component band of component band 1 andthe downlink component band of component band 2 respectively arecommonly associated with PUCCH #2. This makes it possible to preventdata throughput from deteriorating without increasing the amount ofresources required for a control channel in the uplink component band.Furthermore, when consideration is given to a case where a PDCCH may beconfigured using a plurality of CCEs for each terminal or a PDCCHincluding allocation information of uplink data may be configured usingCCEs (that is, when transmission of an ACK/NACK signal in the terminalis unnecessary), the probability that all PUCCHs arranged in the uplinkcomponent band will be used simultaneously is low. Thus, sharing a PUCCHbetween a plurality of component bands makes it possible to improveresource utilization efficiency of the PUCCH.

However, according to the method of sharing a PUCCH arranged in oneuplink component band between a plurality of downlink component bands,CCE allocation to each terminal is limited to avoid collision betweenACK/NACK signals at the base station. For example, an ACK/NACK signalcorresponding to downlink data allocated using a PDCCH made up of CCE #1of a downlink component band of component band 1 is allocated to PUCCH#1 associated with CCE #1. Therefore, when CCE #1 is used for allocationof downlink data in the downlink component band of component band 2,collision occurs between component band 2 and component band 1 in PUCCH#1. For this reason, the base station can no longer allocate CCE #1 incomponent band 2. Furthermore, as described above, since an availableCCE area (search space) is set for each terminal, CCEs to which a PDCCHdirected to each terminal is allocated are further limited.

Particularly, the greater the number of downlink component bands set inthe terminal, the lower is the degree of freedom of CCE allocation tothe terminal in the base station. For example, a case will be describedwhere a search space made up of six CCEs is set for a terminal usingfive downlink component bands and one uplink component band. When aPDCCH is used in 1 CCE units, there are six CCE allocation candidatesdirected to the terminal in a search space of each downlink componentband. Here, when two CCEs of the six CCEs in the search space areallocated to a PDCCH directed to another terminal, four CCEs (remainingCCEs in the search space) can be allocated to the terminal. Therefore,the PDCCH can no longer be allocated to all of five downlink componentbands. Furthermore, since a control channel showing broadcastinformation having higher priority (e.g., BCH: Broadcast Channel) may beallocated to CCEs of the downlink component band, the number of CCEsthat can be allocated in the search space further decreases in thiscase, and data transmission is thereby limited.

It is therefore an object of the present invention to provide a basestation, a terminal and a search space setting method capable offlexibly allocating CCEs without ACK/NACK signals colliding between aplurality of component bands even when performing wideband transmissionon only a downlink.

Solution to Problem

A base station of the present invention adopts a configuration includingan allocation section that sets different search spaces for a pluralityof downlink component bands in a radio communication terminal apparatusthat communicates using the plurality of downlink component bands andallocates resource allocation information of downlink data directed tothe radio communication terminal apparatus to CCEs in the search spaceand a receiving section that extracts a response signal to the downlinkdata from an uplink control channel associated with the CCEs to whichthe resource allocation information is allocated.

A terminal of the present invention is a radio communication terminalapparatus that communicates using a plurality of downlink componentbands and adopts a configuration including a receiving section thatblind-decodes CCEs in different search spaces for the plurality ofdownlink component bands and obtains resource allocation information ofdownlink data directed to the radio communication terminal apparatus anda mapping section that maps a response signal to the downlink data to anuplink control channel associated with the CCEs to which the resourceallocation information is allocated.

A search space setting method of the present invention sets differentsearch spaces for a plurality of downlink component bands in a radiocommunication terminal apparatus that communicates using the pluralityof downlink component bands.

Advantageous Effects of Invention

According to the present invention, even when wideband transmission isperformed using only a downlink, CCEs can be flexibly allocated withoutACK/NACK signals colliding between a plurality of component bands.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 2 is a block diagram illustrating a configuration of a terminalaccording to Embodiment 1 of the present invention;

FIG. 3 is a diagram illustrating PUCCH resources associated with eachCCE according to Embodiment 1 of the present invention;

FIG. 4 is a diagram illustrating component bands set in the terminalaccording to Embodiment 1 of the present invention;

FIG. 5 is a diagram illustrating a method of setting a search space ofeach component band according to Embodiment 1 of the present invention;

FIG. 6 is a diagram illustrating a method of setting a search space ofeach component band according to Embodiment 1 of the present invention;

FIG. 7 is a diagram illustrating a method of setting a search space ofeach component band according to Embodiment 2 of the present invention;

FIG. 8 is a diagram illustrating a method of setting a search spacestart position of each component band according to Embodiment 3 of thepresent invention; and

FIG. 9 is a diagram illustrating another method of setting a searchspace start position of each component band according to Embodiment 3 ofthe present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. The same componentsbetween embodiments will be assigned the same reference numerals andoverlapping explanations will be omitted.

Embodiment 1

FIG.1 is a block diagram illustrating a configuration of base station100 according to the present embodiment.

In base station 100 shown in FIG.1, setting section 101 sets(configures) one or a plurality of component bands to use for an uplinkand a downlink per terminal according to a required transmission rateand amount of data transmission or the like. Setting section 101 thenoutputs setting information including the component band set in eachterminal to control section 102, PDCCH generation section 103 andmodulation section 106.

Control section 102 generates uplink resource allocation informationindicating uplink resources (e.g., PUSCH) to which uplink data of aterminal is allocated and downlink resource allocation informationindicating downlink resources (e.g., PDSCH (Physical Downlink SharedChannel)) to which downlink data directed to the terminal is allocated.Control section 102 then outputs the uplink resource allocationinformation to PDCCH generation section 103 and extraction section 116and outputs the downlink resource allocation information to PDCCHgeneration section 103 and multiplexing section 108. Here, controlsection 102 allocates uplink resource allocation information anddownlink resource allocation information to PDCCHs arranged in downlinkcomponent bands set in each terminal based on the setting informationinputted from setting section 101. To be more specific, control section102 allocates the downlink resource allocation information to PDCCHsarranged in the downlink component bands to be subjected to resourceallocation indicated in the downlink resource allocation information.Furthermore, control section 102 allocates uplink resource allocationinformation to PDCCHs arranged in downlink component bands associatedwith the uplink component bands to be subjected to resource allocationindicated in the uplink allocation information. A PDCCH is made up ofone or a plurality of CCEs.

PDCCH generation section 103 generates a PDCCH signal including theuplink resource allocation information and downlink resource allocationinformation inputted from control section 102. Furthermore, PDCCHgeneration section 103 adds a CRC bit to the PDCCH signal to which theuplink resource allocation information and downlink resource allocationinformation have been allocated and further masks (or scrambles) the CRCbit with the terminal ID. PDCCH generation section 103 then outputs themasked PDCCH signal to modulation section 104.

Modulation section 104 modulates the PDCCH signal inputted from PDCCHgeneration section 103 after channel coding and outputs the modulatedPDCCH signal to allocation section 105.

Allocation section 105 allocates a PDCCH signal of each terminalinputted from modulation section 104 to CCEs in a search space perterminal. Here, allocation section 105 sets different search spaces forthe plurality of downlink component bands in a terminal thatcommunicates using a plurality of downlink component bands and uplinkcomponent bands which are fewer than the plurality of downlink componentbands. For example, allocation section 105 calculates a search space foreach of the plurality of downlink component bands set in each terminalfrom CCE number calculated using a terminal ID of each terminal and ahash function for performing randomization and the number of CCEs (L)making up the search space. Allocation section 105 then outputs thePDCCH signal allocated to the CCEs to multiplexing section 108.Furthermore, allocation section 105 outputs information indicating theCCE to which the PDCCH signal (resource allocation information) isallocated to ACK/NACK receiving section 119.

Modulation section 106 modulates the setting information inputted fromsetting section 101 and outputs the modulated setting information tomultiplexing section 108.

Modulation section 107 modulates inputted transmission data (downlinkdata) after channel coding and outputs the modulated transmission datasignal to multiplexing section 108.

Multiplexing section 108 multiplexes the PDCCH signal inputted fromallocation section 105, the setting information inputted from modulationsection 106 and the data signal (that is, PDSCH signal) inputted frommodulation section 107. Here, multiplexing section 108 maps the PDCCHsignal and data signal (PDSCH signal) to each downlink component bandbased on the downlink resource allocation information inputted fromcontrol section 102. Multiplexing section 108 may also map the settinginformation to a PDSCH. Multiplexing section 108 then outputs themultiplexed signal to IFFT (Inverse Fast Fourier Transform) section 109.

IFFT section 109 transforms the multiplexed signal inputted frommultiplexing section 108 into a time waveform and CP (Cyclic Prefix)adding section 110 adds a CP to the time waveform and thereby obtains anOFDM signal.

RF transmitting section 111 applies radio transmitting processing(up-conversion, digital/analog (D/A) conversion or the like) to the OFDMsignal inputted from CP adding section 110 and transmits the OFDM signalvia antenna 112.

On the other hand, RF receiving section 113 applies radio receivingprocessing (down-conversion, analog/digital (A/D) conversion or thelike) to the received radio signal received in a reception band viaantenna 112 and outputs the received signal obtained to CP removingsection 114.

CP removing section 114 removes a CP from the received signal and FFT(Fast Fourier Transform) section 115 transforms the received signalafter the CP removal into a frequency domain signal.

Extraction section 116 extracts uplink data from the frequency domainsignal inputted from FFT section 115 based on the uplink resourceallocation information inputted from control section 102. IDFT (InverseDiscrete Fourier transform) section 117 then transforms the extractedsignal into a time domain signal and outputs the time domain signal todata receiving section 118 and ACK/NACK receiving section 119.

Data receiving section 118 decodes the time domain signal inputted fromIDFT section 117. Data receiving section 118 outputs the decoded uplinkdata as received data.

ACK/NACK receiving section 119 extracts an ACK/NACK signal from eachterminal corresponding to downlink data (PDSCH signal) of the timedomain signal inputted from IDFT section 117 from a PUCCH associatedwith a CCE used to allocate the downlink data. ACK/NACK receivingsection 119 then makes an ACK/NACK decision on the extracted ACK/NACKsignal. Here, when base station 100 (allocation section 105) allocates aPDCCH signal including downlink resource allocation information ofdownlink data (PDSCH signal) of a plurality of component bands to CCEsof downlink component bands of a plurality of component bands, ACK/NACKreceiving section 119 extracts a plurality of ACK/NACK signals fromPUCCHs associated with CCE numbers of the respective CCEs.

FIG. 2 is a block diagram illustrating a configuration of terminal 200according to the present embodiment. Terminal 200 receives a data signal(downlink data) using a plurality of downlink component bands andtransmits an ACK/NACK signal for the data signal to base station 100using a PUCCH of one uplink component band.

In terminal 200 shown in FIG. 2, RF receiving section 202 is configuredto be able to change a reception band and changes the reception bandbased on band information inputted from setting information receivingsection 206. RF receiving section 202 applies radio receiving processing(down-conversion, analog/digital (A/D) conversion or the like) to thereceived radio signal (here, OFDM signal) received in the reception bandvia antenna 201 and outputs the received signal obtained to CP removingsection 203.

CP removing section 203 removes a CP from the received signal and FFTsection 204 transforms the received signal after the CP removal into afrequency domain signal. The frequency domain signal is outputted todemultiplexing section 205.

Demultiplexing section 205 demultiplexes the signal inputted from FFTsection 204 into a control signal (e.g., RRC signaling) of a higherlayer including setting information, PDCCH signal and data signal (thatis, PDSCH signal). Demultiplexing section 205 outputs the controlinformation to setting information receiving section 206, outputs thePDCCH signal to PDCCH receiving section 207 and outputs the PDSCH signalto PDSCH receiving section 208.

Setting information receiving section 206 reads information indicatinguplink component bands and downlink component bands set in the terminalfrom the control signal inputted from demultiplexing section 205 andoutputs the read information to PDCCH receiving section 207, RFreceiving section 202 and RF transmitting section 215 as bandinformation. Furthermore, setting information receiving section 206reads information indicating the terminal ID set in the terminal fromthe control signal inputted from demultiplexing section 205 and outputsthe read information to PDCCH receiving section 207 as terminal IDinformation.

PDCCH receiving section 207 blind-decodes the PDCCH signal inputted fromdemultiplexing section 205 and obtains a PDCCH signal directed to theterminal. Here, the PDCCH signal is allocated to each CCE (that is,PDCCH) arranged in the downlink component band set in the terminalindicated in the band information inputted from setting informationreceiving section 206. To be more specific, PDCCH receiving section 207calculates a search space of the terminal using the terminal ID of theterminal indicated in the terminal ID information inputted from settinginformation receiving section 206. The search space (CCE numbers of CCEsconstituting the search space) calculated here differs between theplurality of downlink component bands set in the terminal. PDCCHreceiving section 207 then demodulates and decodes the PDCCH signalallocated to each CCE in the calculated search space. PDCCH receivingsection 207 demasks a CRC bit with the terminal ID of the terminalindicated in the terminal ID information for the decoded PDCCH signaland thereby decides the PDCCH signal which results in CRC=OK (no error)to be a PDCCH signal directed to the terminal. PDCCH receiving section207 performs the above described blind decoding on each component bandto which a PDCCH signal has been transmitted and thereby acquiresresource allocation information of the component band. PDCCH receivingsection 207 outputs downlink resource allocation information included inthe PDCCH signal directed to the terminal to PDSCH receiving section 208and outputs uplink resource allocation information to mapping section212. Furthermore, PDCCH receiving section 207 outputs the CCE number ofthe CCE (CCE resulting in CRC=OK) from which the PDCCH signal directedto the terminal is detected to mapping section 212.

PDSCH receiving section 208 extracts received data (downlink data) fromthe PDSCH signal inputted from demultiplexing section 205 based on thedownlink resource allocation information inputted from PDCCH receivingsection 207. Furthermore, PDSCH receiving section 208 performs errordetection on the extracted received data (downlink data). When the errordetection result shows that an error is detected in the received data,PDSCH receiving section 208 generates an NACK signal as the ACK/NACKsignal and generates an ACK signal as the ACK/NACK signal when no erroris detected in the received data. PDSCH receiving section 208 thenoutputs the ACK/NACK signal to modulation section 209.

Modulation section 209 modulates the ACK/NACK signal inputted from PDSCHreceiving section 208 and outputs the modulated ACK/NACK signal to DFT(Discrete Fourier transform) section 211.

Modulation section 210 modulates the transmission data (uplink data) andoutputs the modulated data signal to DFT section 211.

DFT section 211 transforms the ACK/NACK signals inputted from modulationsection 209 and the data signal inputted from modulation section 210into a frequency domain signal and outputs a plurality of frequencycomponents obtained to mapping section 212.

Mapping section 212 maps the frequency component corresponding to thedata signal out of the plurality of frequency components inputted fromDFT section 211 to a PUSCH arranged in the uplink component bandaccording to the uplink resource allocation information inputted fromPDCCH receiving section 207. Furthermore, mapping section 212 maps thefrequency components or code resources corresponding to the ACK/NACKsignals out of the plurality of frequency components inputted from DFTsection 211 to a PUCCH arranged in the uplink component band accordingto the CCE number inputted from PDCCH receiving section 207.

For example, as shown in FIG. 3, PUCCH resources are defined using aprimary spreading sequence (amount of cyclic shift of ZAC (Zero AutoCorrelation) sequence) and a secondary spreading sequence (block-wisespread code) such as Walsh sequence). That is, mapping section 212allocates ACK/NACK signals to primary spreading sequences and secondaryspreading sequences associated with the CCE numbers inputted from PDCCHreceiving section 207. Furthermore, the PUCCH shown in FIG. 3 is sharedbetween a plurality of downlink component bands. Thus, when PDSCHsignals are transmitted in a plurality of downlink component bands,mapping section 212 allocates ACK/NACK signals corresponding to thePDSCH signals transmitted in the respective downlink component bands toPUCCH resources associated with the CCE numbers of CCEs used forallocation of the PDSCH signals. For example, an ACK/NACK signalcorresponding to a PDSCH signal allocated using CCE #0 of a downlinkcomponent band of component band 1 is allocated to a PUCCH resourcecorresponding to CCE #0 shown in

FIG. 3. Likewise, an ACK/NACK signal corresponding to a PDSCH signalallocated using CCE #2 of a downlink component band of component band 2is allocated to a PUCCH resource corresponding to CCE #2 shown in FIG.3.

Modulation section 209, modulation section 210, DFT section 211 andmapping section 212 may be provided for each component band.

IFFT section 213 transforms a plurality of frequency components mappedto the PUSCH into a time domain waveform and CP adding section 214 addsa CP to the time domain waveform.

RF transmitting section 215 is configured to be able to change atransmission band and sets a transmission band based on the bandinformation inputted from setting information receiving section 206. RFtransmitting section 215 then applies radio transmitting processing(up-conversion, digital/analog (D/A) conversion or the like) to theCP-added signal and transmits the signal via antenna 201.

Next, details of operations of base station 100 and terminal 200 will bedescribed.

In the following descriptions, setting section 101 (FIG. 1) of basestation 100 sets two downlink component bands (component band 1 andcomponent band 2) and one uplink component band (component band 1) interminal 200 as shown in FIG. 4. That is, as shown in FIG. 4, settingsection 101 sets both the uplink component band and the downlinkcomponent band for component band 1 in terminal 200, while for componentband 2, setting section 101 does not set any uplink component band(unset) but sets only the downlink component band. That is, base station100 communicates with terminal 200 using two downlink component bandsand one uplink component band, which is one component band fewer thanthe downlink component bands.

Furthermore, as shown in FIG. 4, the PDCCH arranged in each downlinkcomponent band is made up of a plurality of CCEs (CCE #1, CCE #2, CCE#3, ...). Furthermore, as shown in FIG. 4, component band 1 andcomponent band 2 share PUCCHs (e.g., FIG. 3) arranged in the uplinkcomponent band of component band 1. Thus, terminal 200 transmits anACK/NACK signal to base station 100 using a PUCCH arranged in the uplinkcomponent band of component band 1 associated with the CCE used toallocate the PDSCH signal regardless of the component band in which thePDSCH signal has been received.

Here, allocation section 105 allocates a PDCCH signal including downlinkresource allocation information to CCEs in such a way that PUCCHs(ACK/NACK resources) for ACK/NACK signals do not collide between aplurality of downlink component bands. For example, as shown in FIG. 4,a PDCCH signal including downlink resource allocation information (thatis, information indicating PDSCH allocation of component band 1) ofcomponent band 1 is allocated to CCE #1 of the downlink component bandof component band 1. In this case, allocation section 105 allocates aPDCCH signal including downlink resource allocation information (thatis, information indicating PDSCH allocation of component band 2) ofcomponent band 2 to a CCE other than CCE #1 (CCE #2 in FIG. 4) in thedownlink component band of component band 2. On the other hand, when aPDCCH signal including downlink resource allocation information ofcomponent band 1 is allocated to a CCE, allocation section 105 allocatesa PDCCH signal including downlink resource allocation information ofcomponent band 1 to a CCE other than CCE #2 used in the downlinkcomponent band of component band 2. Here, the other terminal in whichthe uplink component band of component band 2 (unset in terminal 200) isset uses a PUCCH arranged in the uplink component band of component band2 to transmit an ACK/NACK signal to base station 100. Thus, in the PUCCHarranged in the uplink component band of component band 1, no collisionoccurs between terminal 200 and the other terminal. For this reason, inthe downlink component band of component band 2, allocation section 105may allocate the PDCCH signal including downlink resource allocationinformation directed to the other terminal to CCE #1 used in componentband 1 (not shown).

Furthermore, allocation section 105 sets different search spaces for theplurality of component bands (component band 1 and component band 2 inFIG. 4) set in terminal 200. That is, allocation section 105 sets aplurality of search spaces according to the number of component bandsset in terminal 200. Allocation section 105 then allocates the PDCCHsignal directed to terminal 200 to CCEs in the search space set for eachcomponent band. Hereinafter, methods 1 and 2 of setting a search spacein allocation section 105 will be described.

<Setting method 1 (FIG. 5)>

In the present setting method, allocation section 105 sets differentsearch spaces for every plurality of component bands so that the searchspaces of the plurality of component bands set in each terminal neighboreach other.

To be more specific, allocation section 105 calculates CCE number S_(n)which is a start position of the search space of n-th component band n(n=1, 2, . . . ) from calculation expression h (N_(UEID)) mod N_(CCE,n)first. Allocation section 105 then sets CCEs of CCE numbers S_(n) to(S_(n)+(L−1)) mod N_(CCE,n) as the search space of component band n.Here, calculation expression h(x) is a hash function for performingrandomization assuming input data as x, N_(UEID) is terminal ID set interminal 200, N_(CCE,n) is the total number of CCEs of component band nand L is the number of CCEs making up a search space. Furthermore,operator “mod” represents a modulo calculation and when the CCE numbercalculated from each relational expression is greater than the totalnumber of CCEs of each component band, mod is returned to initial CCEnumber 0 through a modulo calculation. The same applies to the followingrelational expressions. That is, allocation section 105 sets Lconsecutive CCEs from the start position of the search space as a searchspace of component band n of terminal 200.

Next, allocation section 105 sets CCE number S_(n+1) which is the startposition of the search space of (n+1)-th component band (n+1) in(S_(n)+L) mod N_(CCE,n). Allocation section 105 sets CCEs of CCE numbersto S_(n+1) to (S_(n+1)+(L−1)) mod N_(CCE,n+1) as a search space ofcomponent band (n+1).

Thus, CCE number (S_(n)+(L−1)) mod N_(CCE,n) which is the end positionof the search space of component band n and CCE number (S_(n)+L) modN_(CCE,n) which is the start position of the search space of componentband (n+1) are consecutive CCE numbers. That is, the search space ofcomponent band n and the search space of component band (n+1) are madeup of CCEs of different CCE numbers and further the search space ofcomponent band n and the search space of component band (n+1) areneighboring each other.

To be more specific, as shown in FIG. 5, a case will be described whereCCE number S₁ which is the start position of the search space ofcomponent band 1 is calculated to be CCE #3 from hash functionh(N_(UEID)) mod N_(CCE,n). Here, a case will be described where assumingthe number of CCEs L making up a search space is 6 and the total numberof CCEs of component band 1 N_(CCE,1) and the total number of CCEs ofcomponent band 2 N_(CCE,2) are more than 15 (that is, when the modulocalculation is not taken into consideration in FIG. 5).

Thus, as shown in FIG. 5, allocation section 105 sets CCEs #3 to #8(=(3+(6−1)) mod N_(CCE,1)) as the search space of component band 1.Furthermore, as shown in FIG. 5, allocation section 105 sets the CCEnumber of the start position of the search space of component band 2 to#9(=(3+6) mod N_(CCE,n)) and sets CCEs #9 to #14 (=(9+(6−1)) modN_(CCE,2)) as the search space of component band 2.

As shown in FIG. 5, the search space (CCEs #3 to #8) of component band 1and search space (CCEs #9 to #14) of component band 2 are made up ofCCEs of different CCE numbers. Furthermore, the search space (CCEs #3 to#8) of component band 1 and search space (CCEs #9 to #14) of componentband 2 are neighboring each other. On the other hand, as with allocationsection 105, PDCCH receiving section 207 of terminal 200 identifies thesearch space of component band 1 (CCEs #3 to #8 shown in FIG. 5) and thesearch space of component band 2 (CCEs #9 to #14 shown in FIG. 5) basedon N_(UEID) which is terminal ID of terminal 200. PDCCH receivingsection 207 then blind-decodes only CCEs in the identified search spaceof each component band.

Furthermore, mapping section 212 maps an ACK/NACK signal for a PDSCHsignal (downlink data) allocated using CCEs of a downlink component bandof each component band to a PUCCH associated with the CCEs. For example,in FIG. 5, mapping section 212 maps the ACK/NACK signal corresponding tothe PDSCH signal allocated using one of CCEs #3 to 8 of component band 1to a PUCCH associated with CCEs #3 to #8 (e.g., PUCCHs #3 to #8 (notshown)). On the other hand, in FIG. 5, mapping section 212 maps theACK/NACK signal corresponding to the PDSCH signal allocated using one ofCCEs #9 to 14 of component band 2 to a PUCCH associated with CCEs #9 to#14 (e.g., PUCCHs #9 to #14 (not shown)).

Thus, mapping section 212 maps the ACK/NACK signal corresponding to aPDSCH signal allocated using CCEs of a downlink component band of eachcomponent band to a PUCCH which differs from one component band toanother. That is, no collision of ACK/NACK signal occurs betweencomponent band 1 and component band 2 set in terminal 200. Furthermore,as shown in FIG. 5, suppose, for example, CCEs #0 to #5 of bothcomponent band 1 and component band 2 are used for scheduling of BCH orthe like and CCEs #7 and #8 of component band 1 and CCEs #13 and #14 ofcomponent band 2 are used for terminals other than terminal 200. In thiscase, only CCE #6 can be allocated to terminal 200 within the searchspace set in component band 1. Thus, allocation section 105 allocates aPDCCH signal including resource allocation information of component band1 directed to terminal 200 to CCE #6. On the other hand, CCEs #9 to #12can be allocated within the search space set in component band 2. Thus,allocation section 105 can allocate a PDCCH signal including resourceallocation information of component band 2 directed to terminal 200 toone of CCEs #9 to #12.

That is, in the downlink component band of component band 2, basestation 100 can allocate a PDCCH signal to CCEs without limitation ofCCE allocation in the downlink component band of component band 1(limitation that only CCE #6 can be allocated in FIG. 5). That is, basestation 100 sets different search spaces for the plurality of downlinkcomponent bands set in one terminal. Thus, in the downlink componentband of each component band set in terminal 200, it is possible toperform CCE allocation in each downlink component band without beinglimited by CCE allocation of other different component bands set interminal 200. This allows base station 100 to reduce the possibilitythat a PDCCH signal not being allocated to CCEs may limit datatransmission.

Thus, according to the present setting method, the base station setsdifferent search spaces for the plurality of downlink component bandsset in the terminal. Thus, the terminal can map an ACK/NACK signalcorresponding to a PDSCH signal (downlink data) allocated using CCEs(PDCCH) of different downlink component bands to different PUCCHs forthe plurality of component bands. Therefore, even when widebandtransmission is performed only on the downlink, that is, when narrowbandtransmission is performed on the uplink, the base station can allocatePDCCH signals to CCEs including resource allocation information withoutcausing collision of ACK/NACK signals to occur between component bands.Therefore, according to the present setting method, it is possible toflexibly allocate CCEs without causing collision of ACK/NACK signals tooccur between a plurality of component bands even when widebandtransmission is performed only on the downlink.

Furthermore, according to the present setting method, search spaces forthe plurality of component bands set in the terminal are neighboringeach other. This allows the base station to set search spaces withoutspacing between CCEs used between a plurality of component bands set inthe terminal. For this reason, when, for example, the total number ofCCEs per component band is small or when the number of downlinkcomponent bands set in the terminal is large, the search space ofanother component band (e.g., component band 2 shown in FIG. 5) setbased on the search space of the component band that serves as areference (e.g., component band 1 shown in FIG. 5) is repeatedly setfrom the last CCE to the start CCE. This makes it possible to reduce thepossibility that the other search space will overlap the search space ofthe reference component band (component band 1 shown in FIG. 5).

<Setting method 2 (FIG. 6)>

The present setting method will cause CCE spacing between search spacestart positions of the plurality of component bands set in each terminal(that is, offset of search space start positions) to differ between aplurality of terminals.

As described above, according to setting method 1, search spaces ofcomponent bands from other component band 2 (or component band (n+1))onward are set based on the start position of the search space ofcomponent band 1 (or component band n).

Furthermore, setting method 1 in FIG. 5 randomly sets the start position(CCE number) of the search space of component band 1 based on a hashfunction which receives terminal ID of each terminal as input.Therefore, between a plurality of terminals in which component band 1 isset, the start positions of search spaces of component band 1 set basedon a hash function using their respective terminal IDs may coincide witheach other.

As a result, among terminals having the same start position of searchspace of component band 1, not only the search spaces of component band1 coincides (overlaps), but also all the search spaces of componentbands from component band 2 onward coincide with each other. Therefore,CCE allocation in base station 100 is limited and the degree of freedomof CCE allocation decreases.

Thus, according to the present setting method, allocation section 105causes an offset (CCE spacing) in search space start positions between aplurality of component bands set in respective terminals to differbetween the plurality of terminals. This will be described morespecifically below.

As in the case of setting method 1, allocation section 105 calculatesCCE number S_(n) which is the start position of a search space of n-thcomponent band n (n=1, 2, . . . ) from hash function h(N_(UEID)) modN_(CCE,n) and sets CCEs of CCE numbers S_(n) to (S_(n)+(L−1)) modN_(CCE,n) as the search space of component band n.

Allocation section 105 then sets CCE number S_(n+1) which is the startposition of the search space of (n+1)-th component band (n+1) in(S_(n)+M+L) mod N_(CCE,n). Here, (M+L) is an offset of the startposition of the search space (CCE spacing between the search space startpositions of component band n and component band (n+1)) and M is arandom value which differs from one terminal to another. For example,suppose M=(N_(UEID)) mod (N_(CCE,n)−2L). In this case, since the maximumvalue of M is N_(CCE,n)−2L−1,performing a modulo calculation causes thesearch space of component band (n+1) to return to CCE #0 neveroverlapping the search space of component band n.

Allocation section 105 then sets CCEs of CCE numbers S_(n+1) to(S_(n+1)+(L−1)) mod N_(CCE,n+1) as search spaces of component band (n+1)as with setting method 1.

To be more specific, as shown in FIG. 6, a case will be described wherecomponent band 1 and component band 2 are set in both terminal 1 andterminal 2.Furthermore, suppose CCE number S₁ of the start position ofthe search space of component band 1 set in terminal 1 and terminal 2 isthe same CCE #3. Furthermore, suppose the number of CCEs L that make upthe search space is 6, and M set in terminal 1 is 10 and M set interminal 2 is 18. Thus, suppose offset (M+L) set in terminal 1 is 16 andoffset (M+L) set in terminal 2 is 24. Offset (M+L) set in each terminalmay be notified to each terminal using, for example, a control channelor PDSCH.

Thus, as shown in FIG. 6, allocation section 105 sets CCEs #3 to #8(=(3+(6−1)) mod N_(CCE,1)) as the search space of component band 1 setin terminal 1 and terminal 2 respectively.

Here, since offset (M+L) set in terminal 1 is 16, allocation section 105sets the CCE number of the start position of the search space ofcomponent band 2 set in terminal 1 to #19 (=(3+10+6) mod N_(CCE,n)) asshown in FIG. 6. Allocation section 106 then sets CCE #19 to #24(=(19+(6−1)) mod N_(CCE,2)) as the search space of component band 2 setin terminal 1.

On the other hand, since offset (M+L) set in terminal 2 is 24,allocation section 105 sets the CCE number of the start position of thesearch space of component band 2 set in terminal 2 to #27 (=(3+24) modN_(CCE,n)) as shown in FIG. 6. Allocation section 106 then sets CCEs #27to #32 (=(27+(6−1)) mod N_(CCE,2)) as the search space of component band2 set in terminal 2.

Thus, as shown in FIG. 6, even when the start positions of the searchspaces of component band 1 set in terminal 1 and terminal 2 are the same(when search spaces (CCEs #3 to #8) of component band 1 overlap eachother), the start positions of the search spaces of component band 2 setin terminal 1 and terminal 2 are different. Thus, when, for example,terminal 2 uses all CCEs in the search space of component band 1,terminal 1 cannot use CCEs in the search space of component band 1,whereas terminal 1 can use CCEs in the search space of component band 2.

As shown in FIG. 6, in each terminal, the search space of component band1 and the search space of component band 2 are made up of CCEs ofdifferent CCE numbers as with setting method 1.

On the other hand, as with allocation section 105 according to thepresent setting method, PDCCH receiving section 207 of terminal 200identifies a search space of a component band set in the terminal usingoffset M of the terminal notified from base station 100 andblind-decodes only CCEs in the identified search space of each componentband.

By this means, according to the present setting method, the base stationcauses an offset in the search space start position between a pluralityof component bands set in the terminals to differ from one terminal toanother. Even when search spaces of some component bands overlap withthose of another terminal and CCE allocation is thereby limited, eachterminal is more likely to be able to allocate CCEs without the searchspace of the other component band overlapping the search spaces of theother terminal. That is, according to the present setting method, it ispossible to relax limitations on CCE allocation between a plurality ofterminals and also relax limitations on CCE allocation between aplurality of component bands set in the respective terminals as withsetting method 1. Therefore, according to the present setting method, itis possible to perform CCE allocation more flexibly than arrangementmethod 1.

The methods 1 and 2 of setting search spaces in allocation section 105have been described so far.

Thus, according to the present embodiment, even when widebandtransmission is performed only on a downlink, it is possible to flexiblyperform CCE allocation without collision of ACK/NACK signals between aplurality of component bands.

A case has been described with the present embodiment where the basestation sets a search space of another downlink component band withreference to a downlink component band of component band 1 out of aplurality of downlink component bands. However, the present inventionmay also use an anchor band as a reference component band.

Embodiment 2

In the present embodiment, the base station will set search spaces for aplurality of downlink component bands independently of each other.

Setting section 101 of base station 100 (FIG. 1) according to thepresent embodiment sets different terminal IDs for every plurality ofcomponent bands set in each terminal. Setting section 101 then outputssetting information indicating terminal ID of each component band set ineach terminal to allocation section 105.

Allocation section 105 sets search spaces for every plurality ofcomponent bands set in each terminal using terminal IDs for everyplurality of component bands set in each terminal indicated in settinginformation inputted from setting section 101. To be more specific,allocation section 105 calculates search spaces per component band from

CCE numbers calculated using a hash function which receives terminal IDsset per component band as input and the number of CCEs (L) making up thesearch space.

On the other hand, setting information indicating terminal IDs for everyplurality of component bands set in terminal 200 set by setting section101 of base station 100 is notified to terminal 200 (FIG. 2). PDCCHreceiving section 207 of terminal 200 identifies search spaces ofrespective component bands using terminal IDs per component band set inthe terminal as with allocation section 105. PDCCH receiving section 207blind-decodes CCEs in a search space of each identified component band.

Next, the method of setting search spaces by allocation section 105 willbe described in detail. Here, suppose terminal ID of component band nset by setting section 101 is N_(UEID,n).

Allocation section 105 calculates CCE number S_(n) which is the startpositions of search spaces of a plurality of component bands n (n=1, 2,. . . ) set in terminal 200 from a hash function h(N_(UEID, n)) modN_(CCE,n). Allocation section 105 then sets CCEs of CCE numbers S_(n) to(S_(n)+(L−1)) mod N_(CCE,n) as a search space of component band n.

Thus, search spaces for every plurality of component bands set in eachterminal are set per terminal and per component band independently ofeach other (that is, randomly).

For example, as shown in FIG. 7, a case will be described wherecomponent band 1 and component band 2 are set for both terminal 1 andterminal 2. Here, setting section 101 sets different terminal IDs forcomponent band 1 and component band 2 set in terminal 1. Likewise,setting section 101 sets different terminal IDs for component band 1 andcomponent band 2 set in terminal 2. In FIG. 7, suppose the number ofCCEs L making up a search space is 6.

Allocation section 105 calculates CCE number S₁ which is the startposition of the search space of component band 1 set in terminal 1 froma hash function h(N_(UEID,1)) mod N_(CCE,1) (CCE #3 in FIG. 7).Allocation section 105 sets CCEs (CCE #3 to CCE #8 in FIG. 7) of CCEnumbers S₁ to (S₁+(L−1)) mod N_(CCE,1) as the search space of componentband 1 set in terminal 1. Likewise, allocation section 105 calculatesCCE number S₂ which is the start position of the search space ofcomponent band 2 set in terminal 1 from a hash function h(N_(UEID,2))mod N_(CCE,2) (CCE #9 in FIG. 7). Allocation section 105 then sets CCEs(CCE #9 to CCE #14 in FIG. 7) of CCE numbers S₂ to (S₂+(L−1)) modN_(CCE,2) as the search space of component band 2 set in terminal 1. Forterminal 2, allocation section 105 likewise sets a search space ofcomponent band 1 (CCE #3 to CCE #8 in FIG. 7) and a search space ofcomponent band 2 (CCE #0 to CCE #5 in FIG. 7) independently of eachother.

When allocation section 105 sets search spaces of component band 1 andcomponent band 2 in both terminal 1 and terminal 2 independently of eachother, the search spaces of the respective terminals may overlap eachother in a certain component band (component band 1 in FIG. 7) as shownin FIG. 7. However, since allocation section 105 sets search spaces ofthe respective component bands between terminals and component bandsindependently (irrelevantly) of each other, it is less likely thatsearch spaces of component bands other than a component band in whichsearch spaces of each terminal overlap each other will also overlap eachother. That is, in the search spaces of component bands other than thecomponent bands in which search spaces of each terminal overlap eachother, it is more likely that CCEs can be used without being limited byCCE allocation with other terminals or component bands. Thus, thepresent embodiment can reduce the possibility that data transmissionwill be limited due to limitations on CCE allocation and thereby improvedata throughput.

By this means, according to the present embodiment, the base stationsets search spaces for every plurality of component bands set in eachterminal per component band independently of each other. Even whenwideband transmission is performed only on a downlink, it is therebypossible to flexibly allocate CCEs without collision of ACK/NACK signalsbetween a plurality of terminals and a plurality of component bands.

Embodiment 3

The present embodiment will set search spaces of specific downlinkcomponent bands out of a plurality of downlink component bands based onoutput of a hash function used to set the start positions of searchspaces of downlink component bands other than the specific downlinkcomponent bands.

In the following descriptions, as in the cases of Embodiment 1 andEmbodiment 2, CCEs of CCE numbers S_(n) to (S_(n)+(L−1)) mod N_(CCE,n)are set as a search space of component band n. Furthermore, as shown inFIG. 8, suppose component bands set in terminal 200 (FIG. 2) arecomponent bands 1 to 3. Hereinafter, a method of setting the startposition of a search space per component band will be described.

Allocation section 105 calculates CCE number S_(n) which is the startposition of a search space of component band n set in terminal 200 fromhash function h(N_(UEID)) mod N_(CCE,n). Here, suppose the output resultof hash function h(N_(UEID)) is Y_(n).

Next, allocation section 105 calculates CCE number S_(n) which is thestart position of a search space of component band (n+1) set in terminal200 from hash function h(Y_(n)) mod N_(CCE,n+1). Here, suppose theoutput result of hash function h(Y_(n)) is Y_(n+1).

That is, as shown, for example, in FIG. 8, allocation section 105 setsCCE number S₀ which is the start position of the search space ofcomponent band 1 using output Y₀ of hash function h(terminal ID (thatis, N_(UEID))) in subframe 0. Furthermore, allocation section 105 setsCCE number S₂ which is the start position of the search space ofcomponent band 2 using output Y₁ of hash function h(Y₀) and sets CCEnumber S₃ which is the start position of the search space of componentband 3 using output Y₂ of hash function h(Y₁). That is, allocationsection 105 sets the search space of a specific component band based onthe output of a hash function used to set the start positions of searchspaces of component bands other than the specific downlink componentband.

Thus, allocation section 105 according to the present embodiment sets asearch space per downlink component band using a hash function in thesame way as in Embodiment 2. That is, allocation section 105 accordingto the present embodiment sets search spaces for every plurality ofdownlink component bands independently of (randomly) each other perdownlink component band in the same way as in Embodiment 2.Furthermore,allocation section 105 delivers the output of the hash function used ineach component band to another component band and designates the outputof the hash function as input of a hash function in another componentband between a plurality of component bands (component bands 1 to 3shown in FIG. 8). For this reason, one terminal ID used as input to theinitial (component band 1 of subframe 0 in FIG. 8) hash functionsuffices as terminal ID to be set in each terminal.

Furthermore, allocation section 105 performs the above processing oneach subframe (subframes 0, 1, 2, 3, . . . in FIG. 8). However, as shownin FIG. 8, allocation section 105 calculates a search space startposition of component band 0 of subframe 1 using output Y₃ of hashfunction h (Y₂) which receives output Y₂ of the hash function used tocalculate the search space start position of component band 3 ofsubframe 0 as input. That is, allocation section 105 calculates thestart position of the search space of component band 1 of subframe kusing the output of the hash function used to calculate the search spacestart position of component band N of subframe k−1. Here, N is thenumber of component bands set in the terminal. This causes search spacesto be randomly set between component bands and subframes.

By this means, the present embodiment can obtain effects similar tothose of Embodiment 2, and also eliminates the necessity of setting aplurality of terminal IDs in each terminal, and can thereby reduce thenumber of terminal IDs used for each terminal to a necessary minimum. Itis thereby possible to allocate a sufficient number of terminal IDs tomore terminals in the system. Furthermore, as with LTE, the presentembodiment sets search spaces of different component bands and differentsubframes using one hash function, and can thereby configure a simplebase station and terminal.

In the present embodiment, allocation section 105 may also set searchspaces per component band as shown in FIG. 9 instead of FIG. 8. To bemore specific, as shown in FIG. 9, allocation section 105 calculates thestart positions of search spaces of component bands 1 to 3 in subframe 0as with FIG. 8. Next, as shown in FIG. 9, allocation section 105 usesoutput of a hash function of an immediately preceding subframe of eachcomponent band (that is, subframe 0) as input of a hash function incomponent bands 1 to 3 of subframe 1. That is, allocation section 105delivers the output of the hash function between component bands in aninitial subframe (subframe 0 in FIG. 9) and delivers the output of thehash function between subframes in the same component band from the nextsubframe onward (from subframe 1 onward in FIG. 9). In the initialsubframe shown in FIG. 9, a case has been described where the output ofthe hash function is delivered between component bands. However, as thevalue delivered in the initial subframe, not only the output of the hashfunction but also a value calculated from terminal Id and a componentband number (e.g., value resulting from adding the component band numberto terminal ID) may be delivered between component bands. Thus, basestation 100 can set search spaces in each subframe between terminals andcomponent bands independently of each other as with the presentembodiment (FIG. 8), and can thereby obtain effects similar to those ofEmbodiment 2.

Embodiments of the present invention have been described so far.

A case has been described in the above embodiments where the number ofCCEs occupied by one PDCCH (CCE aggregation level) is one. However, evenwhen one PDCCH occupies a plurality of CCEs (when the CCE aggregationlevel is 2 or more), it is possible to obtain effects similar to thoseof the present invention. Furthermore, it is also possible to calculatesearch spaces according to the CCE aggregation level occupied by onePDCCH and change the number of CCEs L making up a search space dependingon the CCE aggregation level.

Furthermore, CCEs described in the above embodiments are logicalresources and when CCEs are arranged in actual physical time/frequencyresources, CCEs are arranged distributed to all bands in a componentband. Furthermore, CCEs may also be arranged in actual physicaltime/frequency resources distributed to the entire system band (that is,all component bands) as long as CCEs are at least divided per componentband as logical resources.

Furthermore, the present invention may use C-RNTI (Cell-Radio NetworkTemporary Identifier) as a terminal ID.

The present invention may perform a multiplication between bits (thatis, between CRC bits and terminal IDs) or sum up bits and calculate mod2of the addition result (that is, remainder obtained by dividing theaddition result by 2) as masking (scrambling) processing.

Furthermore, a case has been described in the above embodiments where acomponent band is defined as a band having a width of maximum 20 MHz andas a basic unit of communication bands. However, the component band maybe defined as follows. For example, the downlink component band may alsobe defined as a band delimited by downlink frequency band information ina BCH (Broadcast Channel) broadcast from the base station, a banddefined by a spreading width when a PDCCH is arranged distributed in afrequency domain or a band in which an SCH (synchronization channel) istransmitted in a central part. Furthermore, the uplink component bandmay also be defined as a band delimited by uplink frequency bandinformation in a BCH broadcast from the base station or a basic unit ofcommunication band having 20 MHz or less including a PUSCH in thevicinity of the center and PUCCHs (Physical Uplink Control Channel) atboth ends.

Furthermore, although a case has been described in the above embodimentswhere the communication bandwidth of a component band is 20 MHz, thecommunication bandwidth of a component band is not limited to 20 MHz.

Furthermore, band aggregation may also be called “carrier aggregation.”Furthermore, a component band may also be called “unit carrier(component carrier(s))” in LTE. Furthermore, band aggregation is notlimited to a case where continuous frequency bands are aggregated, butdiscontinuous frequency bands may also be aggregated.

Furthermore, a component band of one or a plurality of uplinks set ineach terminal by the base station may be called “UE UL component carrierset” and a component band of a downlink may be called “UE DL componentcarrier set.”

Furthermore, the terminal may also be called “UE” and the base stationmay also be called “Node B or BS (Base Station).” Furthermore, theterminal ID may also be called “UE-ID.”

Moreover, although cases have been described with the embodiments abovewhere the present invention is configured by hardware, the presentinvention may be implemented by software.

Each function block employed in the description of the aforementionedembodiment may typically be implemented as an LSI constituted by anintegrated circuit. These may be individual chips or partially ortotally contained on a single chip. “LSI” is adopted here but this mayalso be referred to as “IC,” “system LSI,” “super LSI” or “ultra LSI”depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells within an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No.2008-281391, filed onOct. 31, 2008, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a mobile communication system orthe like.

1. An integrated circuit configured to control a process, the processcomprising: receiving a first downlink control channel transmitted onone or more control channel element(s) (CCE(s)) in a first search spacethat is comprised of a first plurality of CCEs, the first downlinkcontrol channel including resource assignment information, whichindicates a resource allocated to a terminal apparatus in a componentcarrier n (CCn) out of one or more CC(s); receiving a second downlinkcontrol channel transmitted on one or more CCE(s) in a second searchspace that is comprised of a second plurality of CCE(s), the seconddownlink control channel including resource assignment information,which indicates a resource allocated to the terminal apparatus in acomponent carrier n+1 (CCn+1) out of said one or more CC(s), the firstplurality of CCEs and the second plurality of CCEs are consecutive; andtransmitting an ACK/NACK signal on an uplink control channel, a resourceindex of the uplink control channel being associated with a CCE numberof said one or more CCE(s) in the first search space.
 2. The integratedcircuit according to claim 1, wherein a number of CC(s) configured fordownlink is greater than a number of CC(s) configured for uplink.
 3. Theintegrated circuit according to claim 1, wherein at least one of the oneor more CC(s) configured for downlink is also configured for uplink. 4.The integrated circuit according to claim 1, wherein the first searchspaces and the second search space neighbor each other.
 5. Theintegrated circuit according to claim 1, wherein a CCE number Sn+1,whichdefines a start position of the second search space, is set as (Sn+L)mod NCCE, where a CCE number Sn defines a start position of the firstsearch space, L is a number of the first plurality of CCEs, and NCCE isa total number of CCEs within the CCn.
 6. The integrated circuitaccording to claim 1, wherein a difference between CCE numbers thatrespectively define start positions of the first search space and thesecond search space, varies among a plurality of terminals.
 7. Theintegrated circuit according to claim 1, wherein the first search spaceand the second search space are set independently of each other.
 8. Theintegrated circuit according to claim 1, wherein said transmittingsection is configured to transmit multiple ACK/NACK signals, which arefor the CC and the CCn+1, in one of the CC and the CCn+1.
 9. Theintegrated circuit according to claim 1, wherein the first plurality ofCCEs and the second plurality of CCEs correspond to downlink controlchannel candidates to be decoded by the terminal apparatus.
 10. Theintegrated circuit according to claim 1, wherein each of the firstsearch space and the second search space is comprised of a plurality ofCCEs having consecutive CCE numbers.
 11. The integrated circuit of claim1, comprising: circuitry, which in operation, controls the process; oneor more inputs coupled to the circuitry, which, in operation, receivedownlink control channel signals; and one or more outputs coupled to thecircuitry, which, in operation, output ACK/NACK signals.